Production of a semiconductor device involves a step of forming an electroconductive film on the surface of a wafer to form a wiring layer by photolithography, etching etc., a step of forming an interlaminar insulating film on the wiring layer, etc., and an uneven surface made of an electroconductive material such as metal and an insulating material is generated on the surface of a wafer by these steps. In recent years, processing for fine wiring and multilayer wiring is advancing for the purpose of higher integration of semiconductor integrated circuits, and accordingly techniques of planarizing an uneven surface of a wafer have become important.
As the method of planarizing an uneven surface of a wafer, a CMP method is generally used. CMP is a technique wherein while the surface of a wafer to be polished is pressed against a polishing surface of a polishing pad, the surface of the wafer is polished with an abrasive in the form of slurry having abrasive grains dispersed therein (hereinafter, referred to as slurry). As shown in FIG. 1, a polishing apparatus used generally in CMP is provided for example with a polishing platen 2 for supporting a polishing pad 1, a supporting stand (polishing head) 5 for supporting a polished material (wafer) 4, a backing material for uniformly pressurizing a wafer, and a mechanism of feeding an abrasive. The polishing pad 1 is fitted with the polishing platen 2 for example via a double-sided tape. The polishing platen 2 and the supporting stand 5 are provided with rotating shafts 6 and 7 respectively and are arranged such that the polishing pad 1 and the polished material 4, both of which are supported by them, are opposed to each other. The supporting stand 5 is provided with a pressurizing mechanism for pushing the polished material 4 against the polishing pad 1.
Conventionally, such polishing pads are produced by batch methods such as (1) a method including pouring a resin material into a mold to form a resin block and slicing the resin block with a slicer; (2) a method including pouring a resin material into a mold and pressing the resin material into a thin sheet form; and (3) a method including melting a resin material as a raw material and directly extruding the resin material from a T die into a sheet form. For example, Patent Document 1 discloses that polishing pads are produced by reaction injection molding.
Laminate polishing pads are produced by laminating, with an adhesive or double-side tape, a plurality of resin sheets, such as a polishing layer and a cushion layer, obtained by the method described above, and such a method for production of laminate polishing pads has the problems of a large number of production steps and low productivity rate. Patent Document 2 discloses that in order to solve the problems, laminate polishing pads are produced using an extruder.
A method for continuous production of a polyurethane/polyurea polishing sheet is proposed in order to prevent variations in hardness, gas cell size or the like, which would be caused by batch production methods (see Patent Document 3). Specifically, the method includes mixing a polyurethane material, a fine powder with a particle size of 300 μm or less and an organic foaming agent, ejecting the mixture between a pair of endless plane belts and casting the mixture, then subjecting the mixture to a polymerization reaction with heating means, and separating the resulting sheet-like product from the plane belts to obtain a polishing sheet material.
The polishing surface of polishing pads to be in contact with a substance to be polished is generally provided with grooves for holding and replacing a slurry. The polishing surface of polishing pads made of a foam has a large number of openings and thus has the function of holding and replacing a slurry. The polishing surface provided with grooves allows more efficient holding and replacing of a slurry and can prevent destruction of the polished substance, which is caused by adsorption on the polished substance. In conventional techniques, a polishing sheet is formed, and then the groove is formed by mechanical grinding or laser beam processing of the polishing surface of the polishing sheet. However, such conventional groove-forming processes are time-consuming and thus have the problem of low productivity.
As conventional polishing pads for use in high-precision polishing, polyurethane foam sheets are generally used. Polyurethane foam sheets are excellent in locally planarizing performance but have insufficient cushion performance, and therefore it is difficult to evenly apply a pressure to the entire surface of a wafer from such a polyurethane foam sheet. Thus, another soft cushion layer is generally provided on the back side of such a polyurethane foam sheet to form a laminate polishing pad for use in polishing processes. For example, the laminate polishing pads described below have been developed.
There is disclosed a polishing pad including: a laminate of a first relatively-hard layer and a second relatively-soft layer; and grooves with a certain pitch or projections with a certain form on the polishing surface of the first layer (see Patent Document 4).
It is also disclosed a polishing fabric including: a first sheet-like member having elasticity and irregularities on its surface; and a second sheet-like member that is provided on the surface of the first sheet-like member having irregularities and has a surface for facing the polished surface of an substrate to be treated (see Patent Document 5).
There is also disclosed a polishing pad including a polishing layer and a supporting layer that is laminated on one side of the polishing layer and made of a foam having a compression ratio higher than that of the polishing layer (see Patent Document 6).
However, the conventional laminate polishing pads have a problem in which since they are produced by bonding the polishing layer to the cushion layer with a double-side tape (a pressure-sensitive adhesive layer), a slurry can intrude between the polishing layer and the cushion layer during polishing to reduce the adhesion of the double-side tape so that the polishing layer can be detached from the cushion layer.
There is also disclosed a method for continuously producing a polishing product in which a regularly-shaped composite polishing material is adhered to a substrate (see Patent Document 7). There is further disclosed a method for continuously producing a polishing pad having an underlayer and a polishing layer for the purpose of reducing variation between the polishing pads (see Patent Document 8).
When such CMP is conducted, there is a problem of judging the planarity of wafer surface. That is, the point in time when desired surface properties or planar state are reached should be detected. With respect to the thickness of an oxide film, polishing speed etc., the polishing treatment of a test wafer has been conducted by periodically treating the wafer, and after the results are confirmed, a wafer serving as a product is subjected to polishing treatment.
In this method, however, the treatment time of a test wafer and the cost for the treatment are wasteful, and a test wafer and a product wafer not subjected to processing are different in polishing results due to a loading effect unique to CMP, and accurate prediction of processing results is difficult without actual processing of the product wafer.
Recently, therefore, in order to solve the above problem, there has been a demand for a method capable of detecting in situ the time when the desirable surface characteristics or the desirable thickness is obtained in the CMP process. While various methods are used for such detection, an optical detection method using a mechanism that monitors the film thickness with a laser beam and is incorporated in a rotary platen has been becoming mainstream in view of measurement accuracy and spatial resolution ability of non-contact measurement (see Patent Documents 9 and 10).
Specifically, the optical detection means is a method of irradiating a light beam to a wafer through a window (light transmitting region) and through a polishing pad and monitoring an interference signal produced by the reflection of the light beam to detect the end point of polishing.
At present, a He—Ne laser light having a wavelength light in the vicinity of 600 nm and a white light using a halogen lamp having a wavelength light in 380 to 800 nm is generally used.
In such method, the endpoint is determined by knowing an approximate depth of surface unevenness by monitoring a change in the thickness of a surface layer of a wafer. When such change in thickness becomes equal to the thickness of unevenness, the CMP process is finished. As a method of detecting the endpoint of polishing by such optical means and a polishing pad used in the method, various methods and polishing pads have been proposed.
A polishing pad having, as least a part thereof, a solid and uniform transparent polymer sheet passing a light of wavelengths of 190 to 3500 nm there through is disclosed (see Patent Document 11). Further, a polishing pad having a stepped transparent plug inserted into it is disclosed (see Patent Document 12). A polishing pad having a transparent plug on the same surface as a polishing surface is disclosed (see Patent Document 13).
Besides, a proposal is also offered for preventing a slurry from leaking out an interface (joint line) between a polishing region and a light-transmitting region (see Patent Documents 14 and 15). Even in a case where each of the proposed transparent leakage preventive sheets is provided, however, the slurry is leaked out from the interface therebetween up to the lower part of a polishing layer and accumulated on the leakage preventive sheet to thereby cause a problem in optical detection of an endpoint.
A wire width of an integrated circuit will be hereinafter expected so as to be increasingly narrower in the future tendency of higher integration and leveled-up supper compactness in a semiconductor fabrication and in such a situation, a necessity arises for a high precision optical detection of an endpoint, whereas a conventional detection window for an endpoint has had a problem of the slurry leakage insufficiently solved.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2004-42189    Patent Document 2: JP-A No. 2003-220550    Patent Document 3: JP-A No. 2004-169038    Patent Document 4: JP-A No. 2003-53657    Patent Document 5: JP-A No. 10-329005    Patent Document 6: JP-A No. 2004-25407    Patent Document 7: Japanese Patent Application National Publication (Laid-Open) No. 11-512874    Patent Document 8: Japanese Patent Application National Publication (Laid-Open) No. 2003-516872    Patent Document 9: U.S. Pat. No. 5,069,002    Patent Document 10: U.S. Pat. No. 5,081,421    Patent Document 11: Japanese Patent Application National Publication (Laid-Open) No. 11-512977    Patent Document 12: JP-A No. 9-7985    Patent Document 13: JP-A No. 10-83977    Patent Document 14: JP-A No. 2001-291686    Patent Document 15: Japanese Patent Application National Publication (Laid-Open) No. 2003-510826